The replication of M13 phage carrying insertions in the region of the origin of replication will be investigated by biochemical and biophysical techniques. Foreign DNA will be inserted into the origin region by the use of transposable genetic elements and by direct in vitro insertion at specific restriction sites. Portions of the genome of miniphage which have reiterations of a part of the origin region will be sequenced to determine the precise extent of duplication. We will also attempt to isolate point mutations within the origin by direct mutagenesis of specific restriction fragment carrying the origin and transformation of E. coli cells with heteroduplex molecules in which the mutagenized fragment has been hybridized to circular viral DNA.